Apparatus and method for transceiving channel state information

ABSTRACT

A method of an evolved Node B (eNB) in a wireless environment is provided. The method includes receiving, from a user equipment (UE), a plurality of channel state information (CSI) feedback respectively corresponding to a plurality of CSI processes that are respectively allocated a plurality of precoding matrix indexes (PMIs), determining a modulation and coding scheme (MCS) value based on the plurality of received CSI feedback, and transmitting, to the UE, data modulated based on the determined MCS value by cyclically using the plurality of PMIs, wherein the plurality of CSI feedback may each include information on a channel quality indication (CQI) as to a PMI allocated to a CSI process corresponding to each of the plurality of CSI feedback.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the priority under 35 U.S.C. § 119(a) of aKorean patent application filed on Jun. 16, 2016 in the KoreanIntellectual Property Office and assigned Serial number 10-2016-0074957,the entire disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to wireless communication. Moreparticularly, the present disclosure relates to an apparatus and amethod for transceiving channel state information in a wirelessenvironment.

BACKGROUND

Multiple-input multiple-output (MIMO) technology for transmitting aplurality of information streams in a spatially separated manner is usedfor high-speed data transmission in a wireless environment. MIMOtechnology may be achieved through a closed-loop scheme or an open-loopscheme.

Various schemes for supporting higher mobility of a user equipment (UE)are developing to improve the convenience of users and the portabilityof a UE. For example, a semi-open-loop scheme is in development toguarantee higher mobility of a UE and to supplement the closed-loop (CL)scheme and the open-loop (OL) scheme.

To achieve the semi-open-loop scheme, a novel method for transceivingchannel state information is required.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide an apparatus and a method for transceivingchannel state information for a semi-open-loop scheme in Multiple-inputmultiple-output (MIMO) technology.

In accordance with an aspect of the present disclosure, a method of anevolved Node B (eNB) in a wireless environment is provided. The methodincludes receiving, from a user equipment (UE), a plurality of channelstate information (CSI) feedback respectively corresponding to aplurality of CSI processes that are respectively allocated a pluralityof precoding matrix indexes (PMIs), determining a modulation and codingscheme (MCS) value based on the plurality of received CSI feedback; andtransmitting, to the UE, data modulated based on the determined MCSvalue by cyclically using the plurality of PMIs. The plurality of CSIfeedback each includes information on a channel quality indication (CQI)as to a PMI allocated to a CSI process corresponding to each of theplurality of CSI feedback.

In accordance with another aspect of the present disclosure, anapparatus of an eNB in a wireless environment is provided. The apparatusincludes at least one processor and at least one transceiver configuredto be operatively coupled to the at least one processor. The at leastone processor is configured to receive, from a UE, a plurality of CSIfeedback respectively corresponding to a plurality of CSI processes thatare respectively allocated a plurality of PMIs, determine an MCS valuebased on the plurality of received CSI feedback, and transmit, to theUE, data modulated based on the determined MCS value by cyclically usingthe plurality of PMIs. The plurality of CSI feedback each includesinformation on a CQI as to a PMI allocated to a CSI processcorresponding to each of the plurality of CSI feedback.

In accordance with another aspect of the present disclosure, a method ofa UE in a wireless environment is provided. The method includestransmitting, to an eNB, a plurality of CSI feedback respectivelycorresponding to a plurality of CSI processes that are respectivelyallocated a plurality of PMIs and receiving, from the eNB, datatransmitted by cyclically using the plurality of PMIs. The plurality ofCSI feedback each includes information on a CQI as to a PMI allocated toa CSI process corresponding to each of the plurality of CSI feedback.The data transmitted from the eNB is modulated based on an MCS valuedetermined based on the plurality of CSI feedback.

In accordance with another aspect of the present disclosure, anapparatus of a UE in a wireless environment is provided. The apparatusincludes, at least one processor and at least one transceiver configuredto be operatively coupled to the at least one processor. The at leastone processor is configured to transmit, to an eNB, a plurality of CSIfeedback respectively corresponding to a plurality of CSI processes thatare respectively allocated a plurality of PMIs, and receive, from theeNB, data transmitted by cyclically using the plurality of PMIs. Theplurality of CSI feedback each includes information on a CQI as to a PMIallocated to a CSI process corresponding to each of the plurality of CSIfeedback. The data transmitted from the eNB is modulated based on an MCSvalue determined based on the plurality of CSI feedback.

An apparatus and a method according to various embodiments of thepresent disclosure may implement a semi-open-loop scheme for multipleinput, multiple output (MIMO) by transceiving a CSI feedbackcorresponding to a CSI process that is allocated a PMI and including CQIinformation on the PMI.

Effects which can be acquired by the present disclosure are not limitedto the above described effects, and other effects that have not beenmentioned may be clearly understood by those skilled in the art from thefollowing description.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1A illustrates an example of a closed-loop (CL) multiple-inputmultiple-output (MIMO) system according to an embodiment of the presentdisclosure;

FIG. 1B illustrates an example of an open-loop (OL) MIMO systemaccording to an embodiment of the present disclosure;

FIG. 2 illustrates an example of a semi-OL MIMO system according tovarious embodiments of the present disclosure;

FIG. 3 illustrates an example of a mismatch between a normal channelstate information (CSI) feedback and data transmission according to anembodiment of the present disclosure;

FIG. 4 illustrates an example of a data transceiving process accordingto a multi-CSI feedback according to an embodiment of the presentdisclosure;

FIG. 5 illustrates an example of signal flow between an evolved node B(eNB) and a user equipment (UE) with respect to a multi-CSI feedbackaccording to an embodiment of the present disclosure;

FIG. 6 illustrates an example of a multi-CSI report process depending onwhether to restrict an index indicating a beam group according to anembodiment of the present disclosure;

FIG. 7A illustrates an example of signal flow between an eNB and a UE todetermine a precoding matrix index (PMI) to be restricted according toan embodiment of the present disclosure;

FIG. 7B illustrates another example of signal flow between an eNB and aUE to determine a PMI to be restricted according to an embodiment of thepresent disclosure;

FIG. 8 illustrates an example of signal flow between a UE and an eNBperforming a multi-CSI report process with i1 not restricted accordingto an embodiment of the present disclosure;

FIG. 9 illustrates an example of a functional configuration of a UE thattransmits a multi-CSI report (or feedback) according to an embodiment ofthe present disclosure; and

FIG. 10 illustrates an example of a functional configuration of an eNBthat receives a multi-CSI report according to an embodiment of thepresent disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Such terms as those defined in a generally used dictionary may beinterpreted to have the meanings equal to the contextual meanings in therelevant field of art, and are not to be interpreted to have ideal orexcessively formal meanings unless clearly defined in the presentdisclosure. In some cases, even the term defined in the presentdisclosure should not be interpreted to exclude embodiments of thepresent disclosure.

Hereinafter, in various embodiments of the present disclosure, hardwareapproaches will be described as an example. However, various embodimentsof the present disclosure include a technology that uses both hardwareand software and thus, the various embodiments of the present disclosuremay not exclude the perspective of software.

The present disclosure relates to an apparatus and method fortransceiving channel state information in order to provide asemi-open-loop scheme in a multiple-input-multiple-output (MIMO) system.

As used in the present disclosure, terms to represent controlinformation, terms to represent network entities, terms to representmessages, terms to represent components in an apparatus, and the likeare provided for convenience of description. Therefore, the presentdisclosure is not limited by the following terms, and other terms havingequivalent technical meanings may be applied to the present disclosure.

Although the present disclosure illustrates various embodiments using along term evolution (LTE) system and an LTE-advanced (LTE-A) system,these embodiments are merely examples for description. Variousembodiments of the present disclosure may be easily modified and appliedin other communication systems.

MIMO systems may be classified into a closed-loop (CL) MIMO system andan open-loop (OL) MIMO system depending on whether a transmitterreceives information on a precoding matrix index (PMI) from a receiverwhen generating a transmission beam pattern.

In the OL MIMO system, the receiver may transmit, to the transmitter,channel quality indication (CQI) information including a CQI indexindicating a modulation scheme (for example, quadrature phase shiftkeying (QPSK), 16-quadrature amplitude modulation (16-QAM), and thelike), a code rate, and the like based on time and frequency resourcesand a precoding assumed by specifications.

In the CL MIMO system, the receiver may transmit a PMI feedbackincluding information on a PMI preferred by the receiver to thetransmitter. When the PMI feedback is received, the transmitter maytransmit a signal to the receiver using a transceiving precodingdetermined based on the PMI feedback.

Generally, since a precoding can be selected based on the information onthe PMI preferred by the receiver, the CL MIMO system may have moreefficient system performance than the OL MIMO system.

However, the CL MIMO system requires additional overheads, such as aprocess for the receiver to transmit the PMI feedback to thetransmitter. Further, the CL MIMO system may have performance loss whenthe receiver moves at a very high speed or when a channel between thetransmitter and the receiver significantly changes.

The OL MIMO system may be inferior in system performance to the CL MIMOsystem but may be robust to the impact of dynamic interference. Also,the OL MIMO system does not require additional overhead, such as aprocess of transmitting a PMI feedback.

Accordingly, a semi-OL MIMO system capable of combining advantages ofthe OL MIMO system with advantages of the CL MIMO system has emerged.The semi-OL MIMO system includes a receiver to report part of PMIinformation to a transmitter. The transmitter determines approximatedirectional information for the receiver based on the received part ofPMI information and transmits data by cyclically using a plurality ofprecoders corresponding to the determined approximate directionalinformation. The receiver included in the semi-OL MIMO system may havesmall overheads, as compared with the CL MIMO system, throughtransmission of the part of the PMI information. The transmitterincluded in the semi-OL MIMO system may provide the receiver withhigher-performance spatial multiplexing than the OL MIMO system.Further, the transmitter included in the semi-OL MIMO system may have ahigher diversity gain than the CL MIMO system and may be more robust todynamic interference than the CL MIMO system.

The semi-OL MIMO system with the above-mentioned advantages requiresnew-format procedures for the semi-OL MIMO system. The new-formatprocedures may be easily implemented in a device designed for thesemi-OL MIMO system (for example, a user equipment (UE), an evolved NodeB (eNB), and the like). However, the semi-OL MIMO system may not beefficiently implemented in a device designed without considering thesemi-OL MIMO system.

Accordingly, the present disclosure provides a method for enabling adevice, designed without considering a semi-OL MIMO system, to implementthe semi-OL MIMO system. More particularly, the present disclosureprovides an apparatus and a method for efficiently implementing thesemi-OL MIMO systems through a Channel State information (CSI) feedbackgenerated using a CSI process of an existing LTE or LTE-A system,codebook subset restrictions, and the like.

FIG. 1A illustrates an example of a CL MIMO system according to anembodiment of the present disclosure.

Referring to FIG. 1A, the CL MIMO system 100 may include a UE 110 and aneNB 120.

In operation S110, the UE 110 may report CSI on a channel between the UE110 and the eNB 120 to the eNB 120. The reported CSI may be informationgenerated based on a reference signal transmitted from the eNB 120. Thereported CSI may include PMI information indicating a beam preferred bythe UE 110.

After reporting the CSI including the PMI information indicating thebeam preferred by the UE 110 to the eNB 120, the UE 110 may move to adifferent area in operation S120.

After the UE 110 moves to the different area, the eNB 120 may transmitdata to the UE through a beam determined based on the received PMIinformation in operation S130. However, since the UE 110 has moved tothe different area from an area where the UE 110 reported the CSI, thebeam determined by the eNB 120 may not be the beam preferred by the UE110 located in the different area. That is, since the beam determined bythe eNB 120 is not an optimal beam for the UE 110 located in thedifferent area, the UE 110 may not efficiently receive data transmittedfrom the eNB 120.

As described above, the CL MIMO system 100 may provide an optimal beamto the UE 110 at the time when the UE 110 reports the CSI but may notsupplement the mobility of the UE 110. Therefore, a semi-OL MIMO systemmay be required to supplement the mobility of the UE 110 or the like.

FIG. 1B illustrates an example of an OL MIMO system according to anembodiment of the present disclosure.

Referring to FIG. 1B, the OL MIMO system 150 may include a UE 160 and aneNB 170.

In operation S160, the UE 160 may report CSI on a channel between the UE160 and the eNB 170 to the eNB 170. The reported CSI may be informationgenerated based on a reference signal transmitted from the eNB 170. Thereported CSI may not explicitly include PMI information indicating abeam preferred by the UE 160. The reported CSI includes only a CQI indexindicating a modulation scheme, a code rate, and the like based on timeand frequency resources and a precoding assumed by specifications anddoes not include the PMI information indicating the preferred beam. Whenthe CSI is received, the eNB 170 may estimate at least one beampreferred by the UE 160 based on the reported CSI.

In operation S170, the eNB 170 may transmit data to the UE 160 bycyclically using the estimated at least one beam. The at least one beamis cyclically used for a diversity gain but is not a beam explicitlyselected for the UE 160. Thus, the at least one beam may not be the bestbeam for the UE 160. That is, the UE 160 may not efficiently receive thedata transmitted from the eNB 170.

As described above, the OL MIMO system 150 may provide a beam that isunsuitable for the UE 160. Thus, a semi-OL MIMO system, which has lessoverhead than the CL MIMO system 100 but is capable of supplementing theOL MIMO system 150, may be required.

FIG. 2 illustrates an example of a semi-OL MIMO system according tovarious embodiments of the present disclosure.

Referring to FIG. 2, the semi-OL MIMO system 200 may include a UE 210and an eNB 220.

The UE 210 may be a device capable of communicating with differentpeers. The UE 210 may be a device with mobility. For example, the UE 210may be a mobile phone, a smart phone, a music player, a portable gameconsole, a navigation system, a laptop computer, or the like. The UE 210may also be referred to as a mobile station, a terminal, a station(STA), or the like.

The UE 210 may be located within the coverage of the eNB 220. Also, theUE 210 may be provided with a communication service from the eNB 220.For example, the UE 210 may receive control information from the eNB220. For another example, the UE 210 may transmit data to a differentpeer via the eNB 220. For still another example, the UE 210 may receivedata provided from a server through the eNB 220.

The UE 210 may receive data or control information through atransmission beam of the eNB 220. In some embodiments, the UE 210 mayreceive data or control information transmitted from the eNB 220 througha reception beam of the UE 210. In other embodiments, the UE 210 maytransmit data or control information to the eNB 220 through atransmission beam of the UE 210.

The UE 210 may periodically and/or aperiodically report stateinformation on a current channel between the eNB and the UE 210 to theeNB 220 in order to help the eNB 220 with efficient management of awireless communication system.

The eNB 220 may provide a wireless service to the UE 210.

The eNB 220 may simultaneously transmit multiple data streams for abroadcast service, a multicast service, and/or a unicast service.

The eNB 220 may include at least one cell. The at least one cell is setto one of bandwidths of 1.4 (or 1.25), 3 (or 2.5), 5, 10, 15, and 20megahertz (MHz), and may provide a downlink or uplink transmissionservice to the UE 210. Different cells may be set to provide differentbandwidths. The eNB 220 may control data transmission/reception to/fromthe UE 210. For example, for downlink data, the eNB 220 may transmitdownlink scheduling information to the UE 210, thereby providingtime/frequency regions for transmitting the downlink data, coding, thesize of the downlink data, hybrid automatic repeat and request(HARQ)-related information, and the like.

The eNB 220 may be a fixed device. For example, the eNB 220 may also bereferred to as a base station, an access point, or the like.

The eNB 220 may transmit a reference signal to the UE 210 so that the UE210 may recognize the state of a channel between the UE 210 and the eNB220. In some embodiments, the reference signal may be a channel stateinformation reference signal (CSI-RS). In other embodiments, thereference signal may be a cell-specific reference signal (CRS).

In operation S210, the UE 210 may report, to the eNB 220, CSI generatedbased on a CSI-RS received from the eNB 220. The CSI may include rankindicator (RI) information, PMI information, and CQI information.

The RI information included in the CSI, which is reported to the eNB220, may be information indicating the rank of a channel between the UE210 and the eNB 220. Also, the RI information may indicate the number ofstreams the UE 210 is allowed to receive through the same frequency-timeresource. The RI information may be determined based on long-terminformation and may be fed back to the eNB 220 at periodicity generallylonger than the PMI information and the CQI information.

The PMI information included in the CSI, which is reported to the eNB220, may include PMI information that is simple as compared with normalPMI information (for example, PMI information used in the CL MIMO system100). The simple PMI information may be information indicating anapproximate direction of an area where the UE 210 is located. Forexample, the simple PMI information may include information indicating abeam group including at least one beam preferred by the UE 210 (forexample, a first PMI value i1 or some of the first PMI value and asecond PMI value in a dual structure codebook defined in LTE TS 36.213).

The CQI information included in the CSI, which is reported to the eNB220, may indicate a modulation and a coding rate in which a block errorprobability does not exceed 10% when the eNB 220 uses the reported RIand PMI information. The eNB 220 may indicate theSignal-to-Interference-plus-Noise-Ratio (SINR) of a channel between theeNB and the UE based on the CQI information.

After the UE 210 reports the CSI including the simple PMI information tothe eNB 220, the UE 210 may move to a different area in operation S220.

After the UE 210 moves to the different area, the eNB 220 may transmitdata to the UE 210 by cyclically using beams 230 determined based on thereceived simple PMI information in operation S230. The determined beams230 may be beams included in one beam group. For example, when at leastone determined beam 230 includes a first beam, a second beam, and athird beam, the eNB 220 may transmit the data to the UE 210 bycyclically using the first beam, the second beam, and the third beam.That is, the eNB 220 may transmit the data to the UE 210 based onprecoder cycling.

Although the UE 210 has moved to the different area in operation S220,the UE 210 is located in the coverage of the at least one determinedbeam 230, so that the UE 210 may efficiently receive the data from theeNB 220.

As described above, the semi-OL MIMO system 200 may have less PMIreporting overhead than the CL MIMO system. Further, the semi-OL MIMOsystem 200 may compensate for a loss occurring when the UE 210 moves ata very high speed or when the channel between the UE 210 and the eNB 220drastically changes.

However, when the UE 210 is not designated for the semi-OL MIMO system200 (hereinafter, referred to as a legacy UE), the UE 210 may notefficiently use the semi-OL MIMO system 200. Specifically, when a legacyUE provides an eNB with a normal CSI feedback for a CL MIMO system or anOL MIMO system, precoder cycling performed by the eNB according to thesemi-OL MIMO scheme, and the normal CSI feedback provided to the eNB maymismatch with actual data transmission. The normal CSI feedback mayinclude one PMI and CQI information on one PMI per subband (SB). In someembodiments, the normal CSI feedback may be referred to as a normal CSIreport. Such mismatch may be a term to indicate that a CQI as to aspecific precoder included in the normal CSI feedback provided to theeNB does not correspond with a CQI as to a precoder used in the precodercycling. When the mismatch arises, the eNB cannot help but transmit datato the legacy UE by modulating the data with relatively low transmissionefficiency. Furthermore, since the legacy UE receives the data modulatedwith relatively low transmission efficiency from the eNB, the legacy UEmay not use advantages of the semi-OL MIMO scheme described above.

Therefore, the present disclosure provides a method for the legacy UE toefficiently use a semi-OL MIMO system. Specifically, the presentdisclosure provides a multi-CSI feedback for a semi-OL system as a CSIfeedback defined differently from a normal CSI feedback, for the semi-OLMIMO scheme. The multi-CSI feedback may include a plurality of CSIfeedback corresponding to a plurality of CSI processes, or may alsoinclude a plurality of subframe sets corresponding to one or more CSIprocesses. The plurality of CSI feedback forming the multi-CSI feedbackmay each include information on a PMI assigned for a CSI processcorresponding to each of the plurality of CSI feedback and CQIinformation on the PMI. In some embodiments, the multi-CSI feedback mayalso be referred to as a multi-CSI report. Detailed information on themulti-CSI feedback is provided in the following description.

FIG. 3 illustrates an example of a mismatch between a normal CSIfeedback and data transmission according to an embodiment of the presentdisclosure.

Referring to FIG. 3, i1 may be a factor indicating a precoding matrixW1. For example, i1 may be a first PMI value indicating one beam groupamong a plurality of beam groups. For another example, i1 may be along-term PMI. For still another example, i1 may be a wideband (WB) PMI.For yet another example, i1 may be determined based on i1 for a firstdimension or i1 and i2 for first and second dimensions in atwo-dimensional (2D) antenna array.

i2 may be a second PMI value indicating a precoding matrix W2. Forexample, i2 may be a PMI indicating one of a plurality of beams in thebeam group indicated by i1. For another example, i2 may be a short-termPMI. For still another example, i2 may be a subband (SB) PMI. For yetanother example, i2 may be a PMI (that is, supporting quantizedco-phasing) that is determined based on a phase difference betweenantenna groups having different polarizations of a cross-pol antenna.

An eNB may determine i1 indicating a beam group preferred by a UEaccording to the foregoing procedure. For example, in a Time DivisionDuplex (TDD) system, the eNB may determine i1 for a downlink channelthrough an uplink reference signal transmitted from the UE. For anotherexample, even though an uplink band and a downlink band are positionedas different frequencies due to the use of a band adjacent to the uplinkband as the downlink band, when the eNB is capable of identifyinglong-term channel information on the downlink band through an uplinkreference signal, the eNB may determine i1 through an uplink referencesignal transmitted from the UE. For still another example, the eNB maydetermine i1 through a CSI feedback including information on i1 receivedfrom the UE.

For the semi-OL MIMO scheme, the eNB may restrict some of a plurality ofPMIs respectively indicating the plurality of beams in the beam groupindicated by determined i1 to PMIs for a normal CSI feedback throughcodebook subset restrictions of higher-layer signaling. That is, inorder to transmit data by cyclically using some beams in the beam groupindicated by i1, the eNB may restrict information on PMIs to be includedin the normal CSI feedback to PMI information on some cyclically usedbeams. For example, the UE may restrict i2=0, i2=1, i2=2, and i2=3,among the plurality of PMIs i2=0, i2=1, . . . , i2=k, . . . , i2=n−2,and i2=n−1 respectively indicating the plurality of beams in the beamgroup indicated by i1, to the PMIs for the normal CSI feedback.

The UE may transmit the normal CSI feedback including CQI information onthe restricted PMIs to the eNB. The UE may transmit the normal CSIfeedback in which CQI information on some restricted beams is dividedfor each subband to the eNB. For example, the UE may transmit, to theeNB, the normal CSI feedback including CQI information on i2=0 forsubband 0, CQI information on i2=2 for subband 1, CQI information oni2=0 for subband 2, . . . , and CQI information for i2=1 for subbandN−1.

The eNB may receive the normal CSI feedback transmitted from the UE.Further, the eNB may transmit data to the UE by cyclically using somerestricted beams in the beam group indicated by determined i1 accordingto a designated unit based on the semi-OL MIMO scheme. In someembodiments, the designated unit may be a physical resource block (PRB).In other embodiments, the designated unit may be a precoding resourceblock group (PRG).

The designated unit may vary according to a PMI report (PMI/RIreporting) setting. In transmitting a physical downlink shared channel(PDSCH), the UE receives information necessary for PDSCH decoding anddemodulation reference signal (DMRS) estimation through downlink controlinformation (DCI) using Table 1 below.

TABLE 1 Antenna port(s), scrambling identity, and number of layersindication One Codeword: Two Codewords: Codeword 0 enabled, Codeword 0enabled, Codeword 1 disabled Codeword 1 enable Value Message ValueMessage 0 1 layer, port 7, n_(SCID) = 0 0 2 layers, ports 7-8, n_(SCID)= 0 1 1 layer, port 7, n_(SCID) = 1 1 2 layers, ports 7-8, n_(SCID) = 12 1 layer, port 8, n_(SCID) = 0 2 3 layers, ports 7-9 3 1 layer, port 8,n_(SCID) = 1 3 4 layers, ports 7-10 4 2 layers, ports 7-8 4 5 layers,ports 7-11 5 3 layers, ports 7-9 5 6 layers, ports 7-12 6 4 layers,ports 7-10 6 7 layers, ports 7-13 7 Reserved 7 8 layers, ports 7-14

In multi-user (MU)-MIMO according to the related art, up to twoorthogonal transmission layers are support using 12 DMRS resourceelements (REs) per PRB and an orthogonal cover code (OCC) of length 2considering only antenna ports p=7 and 8. Further, up to fourquasi-orthogonal transmission layers are supported using n_(SCID). TheeNB may indicate an antenna port, n_(SCID), and the number of layers fortransmitting a DMRS using three bits in DCI formats 2C and 2D as inTable 1. In Table 1, a first column shows a case in which a PDSCH isscheduled for transmission with one codeword, and a second column showsa case in which a PDSCH is scheduled for transmission with twocodewords. In the first column, value=4/5/6 is used only for theretransmission of a corresponding codeword.

Thus, referring to Table 1, in MU-MIMO transmission, up to twoorthogonal transmission layers may be supported, and up to fourquasi-orthogonal transmission layers may be supported using n_(SCID).

Accordingly, as described above, the UE may determine the number oflayers allocated for PDSCH transmission, RE mapping, and a referencesignal sequence based on DCI indicated by the eNB through Table 1, andmay estimate a precoded channel, thereby decoding the PDSCH. That is,when no PMI/RI report is set, a corresponding DMRS may be decoded,assuming that the same precoding is always used only in one RB. When aPMI/RI report is set, decoding may be performed, assuming that the sameprecoding is used in one PRG. The size of a PRG unit varies according toa system bandwidth set for the UE and is shown in Table 2 below.

TABLE 2 Size of PRG System Bandwidth PRG Size (P′) (N_(RB) ^(DL)) (PRBs)≤10 1 11-26 2 27-63 3  64-110 2

Therefore, when the PMI/RI report is set, the eNB may cyclically useprecoders necessary for data transmission per PRG. When no PMI/RI reportis set, the eNB may cyclically use precoders necessary for datatransmission per PRB. When cycling is performed per PRG, the eNB mayreceive the PMI and RI reports to identify the direction of acorresponding channel but may have a limited diversity gain due to alarge unit of cycling. When cycling is performed per PRB, the eNB maycyclically use a greater number of precoders due to a small unit ofcycling, thus obtaining a greater diversity gain. However, since the UEdoes not provide information on the rank and direction of a channel, theeNB may need to identify such information through an uplink referencesignal or the like.

For example, the eNB may transmit the data to the UE by cyclically usingi2=0, i2=1, i2=2, and i2=3 respectively indicating some restricted beamsfor each PRB or PRG. The normal CSI feedback transmitted by the UEincludes CQI information on i2=0 only and does not include CQIinformation on i2=1 with respect to subband 0. Also, the normal CSIfeedback transmitted by the UE includes CQI information on i2=2 only anddoes not include CQI information on i2=3 with respect to subband 1. Inaddition, the normal CSI feedback transmitted by the UE includes CQIinformation on i2=1 only and does not include CQI information on i2=0with respect to subband N−1. That is, the normal CSI feedback may causea mismatch in subband 0, subband 1, subband N−1, and the like. Due tothe mismatch, the eNB cannot help but estimate CQI information on i2=1in subband 0, CQI information on i2=3 in subband 1, and CQI informationon i2=0 in subband N−1. The estimated CQI information is only estimatedinformation, which may be inaccurate information. Therefore, the eNBcannot help but transmit data modulated with a relatively low Modulationand Coding Scheme (MCS) value in subbands 0 to N−1. That is, thetransmitted data inevitably has relatively low transmission efficiency.

As described above, when the UE transmits the normal CSI feedback (orthe normal CSI report), the data received by the UE inevitably hasrelatively low transmission efficiency. That is, although the semi-OLMIMO scheme is used for high transmission efficiency, datatransmission/reception between the eNB and the UE may have lowtransmission efficiency. Therefore, a multi-CSI feedback (or a multi-CSIreport) is needed for the semi-OL MIMO scheme with high transmissionefficiency.

FIG. 4 illustrates an example of a data transceiving process accordingto a multi-CSI feedback according to an embodiment of the presentdisclosure.

A UE mentioned in a description of FIG. 4 may be the UE 210 illustratedin FIG. 2, and an eNB mentioned in the description of FIG. 4 may be theeNB 220 illustrated in FIG. 2.

In FIG. 4, the UE may use a plurality of CSI processes for a semi-OLMIMO scheme having high transmission efficiency in an environment wherea CSI report is relatively inaccurate due to a high moving speed and thelike. A CSI process may be a term to indicate an operation of feedingback channel information with an independent CSI-RS resource and anindependent CSI feedback configuration. One or more CSI processes may bepresent in one serving cell. Each of the plurality of CSI processes mayhave an independent CSI-RS resource and an independent feedbackconfiguration. Each of the plurality of CSI processes may be configured,through a codebook subset restriction included in higher-layersignaling, such that the UE reports a PMI that the eNB desires toreceive and a CQI as to the PMI.

Referring to FIG. 4, in operation S410, the eNB may transmit a CSI-RS tothe UE in order to obtain CSI on a channel between the eNB and the UE.The UE may receive the CSI-RS transmitted from the eNB.

Different feedback configurations may be set for the plurality of CSIprocesses. However, the same resource configuration (periodicity andsubframe offset) may be used for the transmission of the CSI-RS. Forsemi-OL MIMO transmission proposed in the present disclosure, each CSIprocess may need to report a different precoder. However, a channelnecessary for channel measurement and transmission may be the same forall CSI processes.

In some embodiments, when a PMI indicating a beam group is determined tobe i1=m through the foregoing procedure or the like, each of theplurality of CSI processes may be configured such that the UE reportsdetermined i1=m, one of i2=k, i2=1, i2=m, and i2=n representing somebeams in a beam group indicated by i1=m, and a CQI as to one of i2=k,i2=1, i2=m, and i2=n. For example, a zeroth CSI process may beconfigured such that the UE reports i1=m, i2=k and a CQI as to i2=k; afirst CSI process may be configured such that the UE reports i1=m, i2=1,and a CQI as to i2=1; a second CSI process may be configured such thatthe UE reports i1=m, i2=m, and a CQI as to i2=m; and a third CSI processmay be configured such that the UE reports i1=m, i2=n, and a CQI as toi2=n. An i2 index configuration may vary depending on an efficientprecoder cycling method (for example, entire i2 cycling, quantizedco-phasing fixing and beam cycling, and beam fixing and quantizedco-phasing cycling) determined by the eNB, the number of CSI processessupportable by the UE, or the like. For example, when the UE supportsfour CSI processes and co-phasing cycling is performed with a first beamin a beam group fixed, i2 may separately be set to 0/1/2/3.

In other embodiments, each of the plurality of CSI processes may beconfigured such that the UE reports i1 having a designated range, one ofi2 values having a designated value, and a CQI as to one of the i2values. For example, a zeroth CSI process may be configured such thatthe UE reports i1 ranging from 0 to n (for example, n may be set to1023), i2=k, and a CQI as to i2=k; a first CSI process may be configuredsuch that the UE reports i1 ranging from 0 to n, i2=k+1, and a CQI as toi2=k+1; a second CSI process may be configured such that the UE reportsi1 ranging from 0 to n, i2=k+2, and a CQI as to i2=k+2; and a third CSIprocess may be configured such that the UE reports i1 ranging from 0 ton, i2=k+3, and a CQI as to i2=k+3.

In operation S420, the UE may transmit, to the eNB, a CSI feedback thatincludes RI information, information on a PMI (W1) indicating a beamgroup, a PMI (W2) indicating a specific beam in the beam group, andinformation (W2/CQI) on a CQI as to the PMI indicating the specific beamand corresponds to a zeroth CSI process. For example, W1 may indicatei1=1, and W2/CQI may indicate i2=0 and CQI information on i2=0. Foranother example, W1 may indicate i1 selected from 0 to 1023, and W2/CQImay indicate i2=0 and CQI information on i2=0.

In operation S430, the UE may transmit, to the eNB, a CSI feedback thatincludes RI information, information on a PMI (W1) indicating a beamgroup, a PMI (W2) indicating a specific beam in the beam group, andinformation (W2/CQI) on a CQI as to the PMI indicating the specific beamand corresponds to a first CSI process. For example, W1 may indicatei1=1, and W2/CQI may indicate i2=1 and CQI information on i2=1. Foranother example, W1 may indicate i1 selected from 0 to 1023, and W2/CQImay indicate i2=1 and CQI information on i2=1.

In operation S440, the UE may transmit, to the eNB, a CSI feedback thatincludes RI information, information on a PMI (W1) indicating a beamgroup, a PMI (W2) indicating a specific beam in the beam group, andinformation (W2/CQI) on a CQI as to the PMI indicating the specific beamand corresponds to a second CSI process. For example, W1 may indicatei1=1, and W2/CQI may indicate i2=2 and CQI information on i2=2. Foranother example, W1 may indicate i1 selected from 0 to 1023, and W2/CQImay indicate i2=2 and CQI information on i2=2.

In operation S450, the UE may transmit, to the eNB, a CSI feedback thatincludes RI information, information on a PMI (W1) indicating a beamgroup, a PMI (W2) indicating a specific beam in the beam group, andinformation (W2/CQI) on a CQI as to the PMI indicating the specific beamand corresponds to a third CSI process. For example, W1 may indicatei1=1, and W2/CQI may indicate i2=3 and CQI information on i2=3. Foranother example, W1 may indicate i1 selected from 0 to 1023, and W2/CQImay indicate i2=3 and CQI information on i2=3.

Although FIG. 4 illustrates the CSI feedback for wideband reporting inoperations S420 to S450, it should be noted that these CSI feedback mayalso be used for subband reporting. In addition, while the above exampleis based on periodic channel state reporting, various embodiments of thepresent disclosure may be used in aperiodic channel state reporting aswell as in periodic channel state reporting.

Further, since the entire band has a common RI configuration for onetransmission in LTE, it may be preferable that the CSI feedback eachhave common RI information for semi-OL MIMO transmission. To this end,an RI reference CSI process may be established through higher-layersignaling, thereby allowing the CSI feedback to report CSI based oncommon RI information. The RI reference CSI process may be aconfiguration for reporting a channel state, assuming the same RI for aplurality of CSI processes.

In operation S460, the eNB may receive a plurality of CSI feedbackrespectively corresponding to the zeroth CSI process to the third CSIprocess from the UE. The plurality of CSI feedback may be collectivelyreferred to as a multi-CSI feedback.

In some embodiments, the plurality of CSI feedback received by the eNBmay respectively include i2=0 to i2=3 and the CQI information on i2=0 tothe CQI information on i2=3 for each subband. Therefore, the eNB mayobtain all of the CQI information on i2=0 to the CQI information on i2=3used for precoder cycling in subband 0 to subband N−1.

In operation S470, the eNB may determine an MCS value for data to betransmitted based on the received multi-CSI feedback. Since the receivedmulti-CSI feedback includes all PMIs and CQI information on the PMIsthat are used for precoder cycling in each subband, the eNB maydetermine the MCS value so that the data to be transmitted has hightransmission efficiency.

In operation S480, the eNB may transmit data modulated based on thedetermined MCS value to the UE through precoder cycling. The eNB maytransmit the data modulated based on the determined MCS value to the UEthrough precoder cycling defined for each designated unit. For example,the designated unit may be an RE, a PRB, a PRG, a subband, or the like.

FIG. 4 shows an example of a multi-CSI feedback including four CSIprocesses. However, this example is provided for illustrative purposes,and the number of CSI processes forming the multi-CSI feedback may varydepending on the number of precoders used in precoder cycling. In someembodiments, when three beams are used for precoder cycling, the numberof CSI processes may be three. In other embodiments, when eightprecoders are used for precoder cycling, a subframe subset may be setthrough higher-layer signaling in addition to the CSI processes.

As described above, in the semi-OL MIMO system, the UE and the eNB mayperform data transmission/reception with high transmission efficiencythrough the multi-CSI feedback. The eNB may obtain CQI information onbeams used for precoder cycling per designated unit through thereception of the multi-CSI feedback. Since the eNB may determine an MCSvalue for data corresponding to one modulation unit based on theexplicit CQI information obtained per designated unit, the eNB mayperform data transmission with high transmission efficiency.

FIG. 5 illustrates an example of signal flow between an eNB and a UEwith respect to a multi-CSI feedback according to an embodiment of thepresent disclosure.

A UE mentioned in a description of FIG. 5 may be the UE 210 illustratedin FIG. 2, and an eNB mentioned in the description of FIG. 5 may be theeNB 220 illustrated in FIG. 2.

Referring to FIG. 5, in operation S510, the eNB 510 and the UE 520 mayperform higher-layer signaling.

For example, the eNB 510 may transmit configuration information relatedto a CSI-RS used for a CSI feedback (or report) to the UE through aradio resource control (RRC) message (or RRC signaling). Theconfiguration information related to the CSI-RS may include thetransmission periodicity (or a duty cycle) of the CSI-RS, the number ofCSI-RS antenna ports, the number of antennas per dimension (for example,N1 and N2), oversampling factor O1 and O2 per dimension, a codebooksubset restriction, a CSI-RS pattern index, a CSI process index, CSI-RStransmit power information, a plurality of resource configurations forsetting one subframe configuration and a position for transmitting aplurality of CSI-RSs, and the like.

For another example, the eNB 510 may transmit configuration informationfor a multi-CSI feedback to the UE through an RRC message. In theconfiguration information for the multi-CSI feedback, PMI/CQIperiodicity and offset, RI periodicity and offset, a WB/SB, a submode,and the like may be set.

In particular, the UE 520 may obtain information on each of CSIprocesses forming the multi-CSI feedback through the procedure ofoperation S510. For example, the UE 520 may obtain information on a PMIto be reported by the UE 520 through each of the CSI processes.

For instance, each of the CSI processes forming the multi-CSI feedbackmay be set as shown in Table 3 below.

TABLE 3 CSI process index i1 index i2 index (layer = 1) 0 0 0 1 0 1 2 02 3 0 3

In Table 3, the CSI process index is a parameter for identifying a CSIprocess, the i1 index is a parameter indicating i1 to be restricted inthe CSI process, the i2 index is a parameter indicating i2 to berestricted in the CSI process. Table 3 may be an example in a case wherei1 to be restricted is determined as 0. A process for determining i1 tobe restricted will be described below in FIGS. 7A and 7B.

According to Table 3, a CSI process having CSI process index 0 (zerothCSI process) is configured such that the UE 520 reports a CQI as to i1having a value of 0 and i2 having a value of 0; a CSI process having CSIprocess index 1 (first CSI process) is configured such that the UE 520reports a CQI as to i1 having a value of 0 and i2 having a value of 1; aCSI process having CSI process index 2 (second CSI process) isconfigured such that the UE 520 reports a CQI as to i1 having a value of0 and i2 having a value of 2; and a CSI process having CSI process index3 (third CSI process) is configured such that the UE 520 reports a CQIas to i1 having a value of 0 and i2 having a value of 3. The indices of0, 1, 2, and 3 allowed to report i2 are for illustrative purposes andmay vary depending on a precoder cycling method (for example, quantizedco-phasing fixing and beam cycling, beam fixing and quantized co-phasingcycling, and the like) determined to be efficient by the eNB.

In operation S520, the eNB 510 may transmit a CSI-RS to the UE 520. TheUE 520 may receive the CSI-RS transmitted from the eNB 510. In the CSIprocesses, there may be a plurality of CSI-RS configurations, but theCSI-RS may be a common configuration to the plurality of CSI processes.In the present disclosure, CSI needed for transmission according to thesemi-OL MIMO scheme requires different PMI assumptions and reports.However, a CSI-RS needed for channel measurement may not need to vary ineach of the plurality of CSI processes, and thus the plurality of CSIprocesses may share a single configuration, thereby minimizing overheadsneeded for CSI-RS transmission and improving system performance. The UE520 may estimate channel information for each antenna port based on thereceived CSI-RS. The UE 520 may estimate an additional channel for avirtual resource based on the estimated channel information for eachantenna port. When this operation is completed, the UE 520 may determineto perform a CSI feedback to the eNB 510. In response to determining toperform the CSI feedback, the UE 520 may generate a PMI, an RI, and aCQI.

In operation S530, the UE 520 may transmit, to the eNB 510, a pluralityof CSI reports respectively corresponding to the plurality of CSIprocesses. That is, the UE 520 may transmit a multi-CSI report to theeNB 510. For example, the UE 520 may transmit a CSI report for thezeroth CSI process, a CSI report for the first CSI process, a CSI reportfor the second CSI process, and a CSI report for the third CSI process.Although four CSI processes are illustrated in operation S530, thenumber of CSI processes for reporting CSI may vary. In operation S530,not only the CSI processes but also a subframe subset may be used toreport a plurality of CSIs by using a different codebook subsetrestriction.

According to embodiments, the transmitted CSI reports may each includedifferent pieces of information. For example, as illustrated above inTable 3, each of the transmitted CSI reports may include information onfixed i1 and i2 designated for each CSI report. For another example, asillustrated below in Table 4, each of the transmitted CSI reports mayinclude information on i1 within a designated range and i2 designatedfor each CSI report.

The CSI reports may each have independent RI information or may have thesame RI information. It may be set through the aforementioned RIreference CSI process whether RI information included in each CSI reportis independent.

In operation S540, the eNB 510 may determine an MCS value for data to betransmitted based on the received multi-CSI feedback. The receivedmulti-CSI report includes all information on a precoder used forprecoder cycling. For example, when the precoder used for precodercycling has an index of i1=1 and indexes of i2=0, i2=2, i2=4 and i2=6,the CSI report for the zeroth CSI process, which forms the receivedmulti-CSI report, may include i1=1, i2=0, and CQI information on i2=0;the CSI report for the first CSI process, which forms the receivedmulti-CSI report, may include i=−1, i2=2, and CQI information on i2=2;the CSI report for the second CSI process, which forms the receivedmulti-CSI report, may include i1=1, i2=4, and CQI information on i2=4;and the CSI report for the third CSI process, which forms the receivedmulti-CSI report, may include i1=1, i2=6, and CQI information on i2=6.Since the eNB 510 obtains all CQI information on the indexes of beamsused for precoder cycling, the eNB 510 may determine the MCS value sothat data may be transmitted with high transmission efficiency.

The precoder information used for precoder cycling may vary per rank.For example, when i2 is restricted in four CSI processes, the processesmay be configured such that i2=0, 1, 2, and 3 are reported when rank=1,and i2=0, 1, 4, and 5 are reported when rank=2.

In operation S550, the eNB 510 may transmit data modulated based on thedetermined MCS value to the UE 520 using precoder cycling. That is, theeNB 510 may transmit the data modulated based on the determined MCSvalue to the UE 520 through the semi-OL MIMO scheme. The UE 520 mayreceive data modulated with an optimized MCS value for the semi-OL MIMOscheme from the eNB 510. That is, a semi-OL MIMO system including theeNB 510 and the UE 520 may cover for dynamic interference or high-speedmovements of the UE 520 with less overheads than the CL MIMO system.

As described above, the semi-OL MIMO scheme may compensate weak pointsof the CL MIMO scheme and weak points of the OL MIMO scheme by usingapproximate direction information on the UE and precoder cycling. Here,the approximate direction information on the UE may be determinedthrough various methods. For example, the approximate directioninformation on the UE may be determined through a PMI indicating onebeam group (for example, i1) among a plurality of beam groups.Accordingly, various embodiments according to whether to restrict thePMI indicating the one beam group will be described below.

FIG. 6 illustrates an example of a multi-CSI report process depending onwhether to restrict an index indicating a beam group according to anembodiment of the present disclosure.

A UE mentioned in a description of FIG. 6 may be the UE 210 illustratedin FIG. 2, and an eNB mentioned in the description of FIG. 6 may be theeNB 220 illustrated in FIG. 2.

Referring to FIG. 6, in operation S610, the eNB may determine whether torestrict a PMI indicating a beam group (hereinafter, i1) for a multi-CSIreport process for the semi-OL MIMO scheme. When the eNB desires toobtain information on i1, which is a parameter indicating approximatedirection information on the UE, through an independent procedure, andthen to start (or trigger) the multi-CSI report process, the eNB mayperform operation S620. Alternatively, when the eNB desires to perform aprocedure for obtaining information on i1, which is a parameterindicating approximate direction information on the UE, and a multi-CSIreport process through one procedure, the eNB performs operation S640.

In operation S620, the eNB may determine i1 to be restricted. Forexample, the eNB may determine i1 to be restricted through anindependent procedure of the multi-CSI report process. In someembodiments, the eNB may determine i1 to be restricted based on anuplink reference signal transmitted from the UE. In other embodiments,the eNB may determine i1 to be restricted via a codebook subsetrestriction and a single CSI process.

In operation S630, the eNB may trigger a first multi-CSI report processbased on determined i1. For example, the eNB may set a CSI process forrestricting some beams included in a beam group indicated by determinedi1 through a codebook subset restriction in order to trigger the firstmulti-CSI report process. For another example, the eNB may set, with theUE, the transmission periodicity and the transmission offset of each ofCSI reports forming a first multi-CSI report to the UE, in order totrigger the first multi-CSI report process. The first multi-CSI reportprocess may allow the UE to report different i2 for each CSI processbased on the same i1.

In operation S640, the eNB may trigger a second multi-CSI report processcapable of restricting i1 through one procedure. For example, the eNBmay set a CSI process for restricting i1 and i2 through a codebooksubset restriction in order to trigger the second multi-CSI reportprocess. In the second multi-CSI report process, the UE reportsdifferent i2 based on different i1. However, when characteristics of along-term channel between the eNB and the UE change, no RRCre-establishment may be required.

FIG. 7A illustrates an example of signal flow between an eNB and a UE todetermine a PMI to be restricted according to an embodiment of thepresent disclosure.

A UE mentioned in a description of FIG. 7A may be the UE 210 illustratedin FIG. 2, and an eNB mentioned in the description of FIG. 7A may be theeNB 220 illustrated in FIG. 2.

Referring to FIG. 7A, in operation S710, the UE 720 may transmit anuplink reference signal to the eNB 710. For example, the uplinkreference signal may be a sounding reference signal (SRS). The eNB 710may receive the uplink reference signal from the UE 720.

In operation S720, the eNB 710 may determine the state of an uplinkchannel between the eNB 710 and the UE 720 based on the received uplinkreference signal. The eNB 710 may determine the state of the uplinkchannel between the eNB 710 and the UE 720 in order to determine thestate of a downlink channel between the eNB 710 and the UE 720. Forexample, since a TDD system performs uplink transmission and downlinktransmission in the same frequency band (that is, the TDD system haschannel reciprocity), the eNB 710 may determine the state of thedownlink channel based on the state of the uplink channel. For anotherexample, when an uplink band and a downlink band are contiguous in anFDD system, since the uplink channel and the downlink channel havechannel reciprocity, the eNB 710 may determine the state of the downlinkchannel based on the state of the uplink channel.

In operation S730, the eNB 710 may determine the state of the downlinkchannel based on the determined state of the uplink channel.

In operation S740, the eNB 710 may determine i1 to be restricted basedon the determined state of the downlink channel. For example, the eNB710 may determine information on an approximate direction of the UEbased on the determined state of the downlink channel. The eNB 710 maydetermine a PMI corresponding to the determined approximate direction asi1 to be restricted.

FIG. 7B illustrates another example of signal flow between an eNB and aUE to determine a PMI to be restricted according to an embodiment of thepresent disclosure.

A UE mentioned in a description of FIG. 7B may be the UE 210 illustratedin FIG. 2, and an eNB mentioned in the description of FIG. 7B may be theeNB 220 illustrated in FIG. 2.

Referring to FIG. 7B, in operation S750, the eNB 760 and the UE 770 mayperform higher-layer signaling. In some embodiments, the eNB 760 mayconfigure a CSI process through a codebook subset restriction. The CSIprocess may be configured such that the UE reports specified PMIindices. For example, the CSI process may be configured as below inTable 4.

TABLE 4 CSI process index i1 index i2 index (layer = 1) 0 0-1023 0

In Table 4, the CSI process index is a parameter for identifying a CSIprocess, the i1 index is a parameter indicating i1 to be restricted inthe CSI process, the i2 index is a parameter indicating i2 to berestricted in the CSI process. In Table 4, a CSI process with a CSIprocess index of 0 may be a CSI process configured such that the UE 770reports a CQI as to i1 ranging from 0 to 1023 and i2=0.

Although Table 4 shows i1 ranging from 0 to 1023, it should be notedthat the range of i1 may be variously set (different CSI-RS portnumbers, N1/N2, O1/O2, and the like) depending on embodiments.

In operation S760, the eNB 760 may transmit a CSI-RS to the UE 770. TheUE 770 may receive the CSI-RS from the eNB 760. The UE 770 may generatea CSI report corresponding to the CSI process indicated by the CSIprocess index of 0 based on the received CSI-RS. The generated CSIreport may include CQI information on each of i1=0 to i1=1023 and i2=0.In addition, the generated CSI report may include RI information.

In operation S770, the UE 770 may transmit the generated CSI report forthe CSI process to the eNB 760. The eNB 760 may receive the CSI reportfrom the UE 770.

In operation S780, the eNB 760 may determine an approximate direction ofthe UE 770 based on the received CSI report. Since the received CSIreport includes the CQI information for each of i1=0 to i1=1023 andi2=0, the eNB 760 may determine a PMI indicating the approximatedirection of the UE 770 as i1 to be restricted. For example, a CQI as toi1=k is determined to be the best among the CQI information on each ofi1=0 to i1=1023, the eNB 760 may determine i1=k as a PMI to berestricted.

FIG. 8 illustrates an example of signal flow between a UE and an eNBperforming a multi-CSI report process with i1 not restricted accordingto an embodiment of the present disclosure.

A UE mentioned in a description of FIG. 8 may be the UE 210 illustratedin FIG. 2, and an eNB mentioned in the description of FIG. 8 may be theeNB 220 illustrated in FIG. 2.

Referring to FIG. 8, in operation S810, the eNB 810 and the UE 820 mayperform higher-layer signaling.

For example, the eNB 810 may transmit configuration information relatedto a CSI-RS used for a CSI report to the UE 820 through an RRC message.For another example, the eNB 810 may transmit configuration informationfor a multi-CSI feedback to the UE 820 through an RRC message.

Through operation S810, the UE 820 may obtain information on each of CSIprocesses forming a multi-CSI report. For example, the UE 820 may obtaininformation on a PMI to be reported by the UE 820 through each of theCSI processes.

For example, each of the CSI processes forming the multi-CSI report maybe configured as below in Table 5.

TABLE 5 CSI process index i1 index i2 index (layer = 1) 0 0-1023 0 10-1023 1 2 0-1023 2 3 0-1023 3

In Table 5, the CSI process index is a parameter for identifying a CSIprocess, the i1 index is a parameter indicating i1 to be restricted inthe CSI process, the i2 index is a parameter indicating i2 to berestricted in the CSI process.

For example, when the eNB 810 fails to obtain information on i1indicating an approximate direction of the UE 820, the eNB 810 needs notonly a PMI report for precoder cycling but also the information on i1indicating the approximate direction of the UE 820 and the state of along-term channel between the UE 820 and the eNB 810.

In Table 5, in order to identify the information on i1, a CSI processhaving CSI process index 0 (zeroth CSI process) is configured such thatthe UE 820 reports a CQI as to i1 having a value ranging from 0 to 1023and i2 having a value of 0; a CSI process having CSI process index 1(first CSI process) is configured such that the UE 820 reports a CQI asto i1 having a value ranging from 0 to 1023 and i2 having a value of 1;a CSI process having CSI process index 2 (second CSI process) isconfigured such that the UE 820 reports a CQI as to i1 having a valueranging from 0 to 1023 and i2 having a value of 2; and a CSI processhaving CSI process index 3 (third CSI process) is configured such thatthe UE 820 reports a CQI as to i1 having a value ranging from 0 to 1023and i2 having a value of 3.

Although Table 5 shows i1 ranging from 0 to 1023, it should be notedthat the range of i1 may be variously set (different CSI-RS portnumbers, N1/N2, O1/O2, and the like) depending on embodiments.

When the CSI processes are configured as shown in Table 5, the eNB 810may obtain approximate direction information on the UE 820 and CQIinformation on each beam used for precoder cycling through a subsequentprocedure (that is, a second multi-CSI report process).

In operation S820, the eNB 810 may transmit a CSI-RS to the UE 820. Theconfiguration information related to the CSI-RS may be recognized by theUE 820 through operation S810. Therefore, the UE 820 may receive theCSI-RS from the eNB 810.

The UE 820 may generate CSI reports for the respective CSI processesbased on the configuration information on the multi-CSI report set inoperation S810 and the received CSI-RS. For example, a CSI reportcorresponding to the zeroth CSI process may include i1 having a valueranging from 0 to 1023, i2 having a value of 0, and CQI information oni2 having a value of 0; a CSI report corresponding to the first CSIprocess may include i1 having a value ranging from 0 to 1023, i2 havinga value of 1, and CQI information on i2 having a value of 1; a CSIreport corresponding to the second CSI process may include i1 having avalue ranging from 0 to 1023, i2 having a value of 2, and CQIinformation on i2 having a value of 2; and a CSI report corresponding tothe third CSI process may include i1 having a value ranging from 0 to1023, i2 having a value of 3, and CQI information on i2 having a valueof 3.

The eNB 810 may receive the CSI reports from the UE 820.

The CSI reports respectively corresponding to the zeroth to third CSIprocesses may have different values of i1. As shown in Table 5, sincethe second multi-CSI report process does not restrict i1 to one value,the CSI reports may have different values of i1. In this case, the eNB810 may transmit data based on different i1. Further, the eNB 810 maynot accurately re-estimate i1 information and i2 information needed fordata transmission through the semi-OL MIMO scheme.

Thus, the eNB 810 may receive, for example, the CSI report correspondingto the first CSI process, which may include i1=k, and the CSI reportcorresponding to the second CSI process, which may include i1=k+2. WhenCSI reports having different values of i1 are received, the eNB 810 mayperform the procedure described with reference to FIG. 7A or 7B and theprocedure described with reference to FIG. 5, instead of performingoperation S840, for the semi-OL MIMO scheme having accurate channelestimation or high transmission efficiency.

In operation S840, the eNB 810 may determine an MCS value for data to betransmitted based on the received CSI reports. Since the eNB 810acquires CQI information on each subband and each PMI through theprocedures of S810 to S830, the eNB 810 may determine an optimized MCSvalue for data transmission.

In operation S850, the eNB 810 may transmit data modulated based on thedetermined MCS value to the UE 820 through precoder cycling. Forexample, the data may be transmitted to the UE 820 via a PhysicalDownlink Shared Channel (PDSCH). The UE 820 may receive the datatransmitted through precoder cycling from the eNB 810.

FIG. 9 illustrates an example of a functional configuration of a UE thattransmits a multi-CSI report (or feedback) according to an embodiment ofthe present disclosure.

The functional configuration may be included in any one of the UEs shownin FIGS. 2 to 5 and FIGS. 7A, 7B and 8.

Referring to FIG. 9, a UE 900 may include an antenna 910, acommunication unit 920, a controller 925, and a storage unit 930.

The antenna 910 may include one or more antennas. The antenna 910 may besuitably configured for an MIMO scheme.

The communication unit 920 may perform functions of transmitting orreceiving a signal through a wireless channel.

The communication unit 920 may perform a function of conversion betweena baseband signal and a bit string according to a physical-layerspecification of a system. For example, in data transmission, thecommunication unit 920 may encode and modulate a transmission bit stringto generate complex symbols. For another example, in data reception, thecommunication unit 920 may demodulate and decode a baseband signal toreconstruct a reception bit string.

The communication unit 920 may upconvert a baseband signal to a radiofrequency (RF) band signal and may transmit the RF band signal throughthe antenna 910. The communication unit 920 may downconvert an RF bandsignal, which is received through the antenna 910, to a baseband signal.For example, the communication unit 920 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, adigital-to-analog converter (DAC), an analog digital converter (ADC), orthe like.

The communication unit 920 may be operatively coupled with thecontroller 925.

The communication unit 920 may include at least one transceiver.

The controller 925 may control overall operations of the UE 900. Forexample, the controller 925 may transmit or receive a signal through thecommunication unit 920. The controller 925 may record data in thestorage unit 930 and may read data stored in the storage unit 930. Tothis end, the controller 925 may include at least one processor. Forexample, the controller 925 may include a communication processor (CP)performing a control for communication and an application processor (AP)controlling a higher layer, such as an application program.

The controller 925 may be configured to implement the procedures and/ormethods proposed in the present disclosure.

The storage unit 930 may store a control command code, control data, oruser data to control the UE 900. For example, the storage unit 930 mayinclude an application, an operating system (OS), a middleware, and adevice driver.

The storage unit 930 may include at least one of a volatile memory and anon-volatile memory. The volatile memory may include a dynamicrandom-access memory (DRAM), a static RAM (SRAM), a synchronous DRAM(SDRAM), a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistiveRAM (RRAM), a ferroelectric RAM (FeRAM), and the like. The non-volatilememory may include a read-only memory (ROM), a programmable ROM (PROM),an electrically programmable ROM (EPROM), an electrically erasable ROM(EEPROM), a flash memory, and the like.

The storage unit 930 may include a non-volatile medium, such as a harddisk drive (HDD), a solid state disk (SSD), an embedded multi media card(eMMC), and a universal flash storage (UFS).

The storage unit 930 may be operatively coupled to the controller 925.

FIG. 10 illustrates an example of a functional configuration of an eNBthat receives a multi-CSI report according to an embodiment of thepresent disclosure.

The functional configuration may be included in any one of the eNBsshown in FIGS. 2 to 6, 7A, 7B, and 8.

Referring to FIG. 10, an eNB 1000 may include an antenna 1010, acommunication unit 1020, a controller 1025, and a storage unit 1030.

The antenna 1010 may include one or more antennas. The antenna 1010 maybe suitably configured for an MIMO scheme.

The communication unit 1020 may perform functions of transmitting orreceiving a signal through a wireless channel.

The communication unit 1020 may perform a function of conversion betweena baseband signal and a bit string according to a physical-layerspecification of a system. For example, in data transmission, thecommunication unit 1020 may encode and modulate a transmission bitstring to generate complex symbols. For another example, in datareception, the communication unit 1020 may demodulate and decode abaseband signal to reconstruct a reception bit string.

The communication unit 1020 may upconvert a baseband signal to an RFband signal and may transmit the RF band signal through the antenna1010. The communication unit 1020 may downconvert an RF band signal,which is received through the antenna 1010, to a baseband signal. Forexample, the communication unit 1020 may include a transmission filter,a reception filter, an amplifier, a mixer, an oscillator, adigital-to-analog converter (DAC), an analog digital converter (ADC), orthe like.

The communication unit 1020 may be operatively coupled with thecontroller 1025.

The communication unit 1020 may include at least one transceiver.

The controller 1025 may control overall operations of the eNB 1000. Forexample, the controller 1025 may transmit or receive a signal throughthe communication unit 1020. The controller 1025 may record data in thestorage unit 1030 and may read data stored in the storage unit 1030. Tothis end, the controller 1025 may include at least one processor. Forexample, the controller 1025 may include a CP performing a control forcommunication and an AP controlling a higher layer, such as anapplication program.

The controller 1025 may be configured to implement the procedures and/ormethods proposed in the present disclosure.

The storage unit 1030 may store a control command code, control data, oruser data to control the eNB 1000. For example, the storage unit 1030may include an application, an Operating System (OS), a middleware, anda device driver.

The storage unit 1030 may include at least one of a volatile memory anda non-volatile memory. The volatile memory may include a DynamicRandom-Access Memory (DRAM), a Static RAM (SRAM), a Synchronous DRAM(SDRAM), a Phase-change RAM (PRAM), a Magnetic RAM (MRAM), a ResistiveRAM (RRAM), a Ferroelectric RAM (FeRAM), and the like. The non-volatilememory may include a Read-Only Memory (ROM), a Programmable ROM (PROM),an Electrically Programmable ROM (EPROM), an Electrically Erasable ROM(EEPROM), a flash memory, and the like.

The storage unit 1030 may include a non-volatile medium, such as a HardDisk Drive (HDD), a Solid State Disk (SSD), an embedded Multi Media Card(eMMC), and a Universal Flash Storage (UFS).

The storage unit 1030 may be operatively coupled to the controller 1025.

In the present disclosure, particular operations described as beingperformed by an eNB may be performed by an upper node than the eNBdepending on embodiments. That is, it would be apparent that variousoperations implemented for communication with a UE in a networkincluding a plurality of network nodes including an eNB may be performedby the eNB or network nodes other than the eNB.

Methods according to embodiments stated in claims and/or specificationsof the present disclosure may be implemented in hardware, software, or acombination of hardware and software.

When the methods are implemented by software, a computer-readablestorage medium for storing one or more programs (software modules) maybe provided. The one or more programs stored in the computer-readablestorage medium may be configured for execution by one or more processorswithin the electronic device. The at least one program may includeinstructions that cause the electronic device to perform the methodsaccording to various embodiments of the present disclosure as defined bythe appended claims and/or disclosed herein.

The programs (software modules or software) may be stored innon-volatile memories including a random access memory and a flashmemory, a ROM, an EEPROM, a magnetic disc storage device, a compactdisc-ROM (CD-ROM), digital versatile discs (DVDs), or other type opticalstorage devices, or a magnetic cassette. Alternatively, any combinationof some or all of the may form a memory in which the program is stored.Further, a plurality of such memories may be included in the electronicdevice.

In addition, the programs may be stored in an attachable storage devicewhich may access the electronic device through communication networkssuch as the Internet, Intranet, local area network (LAN), wide LAN(WLAN), and storage area network (SAN) or a combination thereof. Such astorage device may access the electronic device via an external port.Further, a separate storage device on the communication network mayaccess a portable electronic device.

In the above-described detailed embodiments of the present disclosure, acomponent included in the present disclosure is expressed in thesingular or the plural according to a presented detailed embodiment.However, the singular form or plural form is selected for convenience ofdescription suitable for the presented situation, and variousembodiments of the present disclosure are not limited to a singleelement or multiple elements thereof. Further, either multiple elementsexpressed in the description may be configured into a single element ora single element in the description may be configured into multipleelements.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of an evolved node B (eNB) in a wirelessenvironment, the method comprising: receiving, from a user equipment(UE), a plurality of channel state information (CSI) feedbackrespectively corresponding to a plurality of CSI processes that arerespectively allocated a plurality of precoding matrix indexes (PMIs),the plurality of CSI feedback each comprising information on a channelquality indication (CQI) as to a PMI allocated to a CSI processcorresponding to each of the plurality of CSI feedback; determining amodulation and coding scheme (MCS) value based on the plurality ofreceived CSI feedback including information on CQIs for all of theplurality of PMIs that are used for PMI cycling in each subband; andtransmitting, to the UE, data modulated based on the determined MCSvalue by cyclically using the plurality of PMIs.
 2. The method of claim1, wherein the plurality of PMIs is respectively allocated to theplurality of CSI processes based on a radio resource control (RRC)message comprising information on a codebook subset restriction.
 3. Themethod of claim 1, further comprising: determining one first PMI among aplurality of first PMIs respectively indicating a plurality of beamgroups, wherein the plurality of PMIs comprises some of a plurality ofsecond PMIs respectively indicating beams comprised in a beam groupindicated by the determined first PMI.
 4. The method of claim 3, whereinthe determining of the one first PMI comprises: determining a state of adownlink between the eNB and the UE based on an uplink reference signalreceived from the UE when the eNB operates in a time division duplex(TDD) mode; and determining the one first PMI among the plurality offirst PMIs based on the determined state of the downlink.
 5. The methodof claim 3, wherein the determining of the one first PMI comprises:receiving, from the UE, a plurality of different CSI feedbackrespectively corresponding to a plurality of different CSI processesthat are respectively allocated the plurality of first PMIs; anddetermining the one first PMI among the plurality of first PMIs based onthe plurality of received different CSI feedback, wherein the pluralityof different CSI feedback each comprises information on a CQI as to theone first PMI allocated to a different CSI process corresponding to eachof the plurality of different CSI feedback.
 6. The method of claim 1,further comprising: transmitting a CSI reference signal (CSI-RS) to theUE, wherein each of the plurality of CSI feedback is generated based onthe CSI-RS.
 7. The method of claim 1, wherein the transmitting of thedata modulated based on the determined MCS value to the UE comprisestransmitting, to the UE, the data modulated based on the determined MCSvalue by cyclically using the plurality of PMIs based on a designateddevice, and wherein the designated device is set to one of a physicalresource block (PRB) or a precoding resource block group (PRG).
 8. Anapparatus of an evolved node B (eNB) in a wireless environment, theapparatus comprising: at least one processor; and at least onetransceiver configured to be operatively coupled to the at least oneprocessor, wherein the at least one processor is configured to: receive,from a user equipment (UE), a plurality of channel state information(CSI) feedback respectively corresponding to a plurality of CSIprocesses that are respectively allocated a plurality of precodingmatrix indexes (PMIs), the plurality of CSI feedback each comprisinginformation on a channel quality indication (CQI) as to a PMI allocatedto a CSI process corresponding to each of the plurality of CSI feedback,determine a modulation and coding scheme (MCS) value based on theplurality of received CSI feedback including information on CQIs for allof the plurality of PMIs that are used for PMI cycling in each subband,and transmit, to the UE, data modulated based on the determined MCSvalue by cyclically using the plurality of PMIs.
 9. The apparatus ofclaim 8, wherein the plurality of PMIs is respectively allocated to theplurality of CSI processes based on a radio resource control (RRC)message comprising information on a codebook subset restriction.
 10. Theapparatus of claim 8, wherein the at least one processor is furtherconfigured to determine one first PMI among a plurality of first PMIsrespectively indicating a plurality of beam groups, and wherein theplurality of PMIs comprises some of a plurality of second PMIsrespectively indicating beams comprised in a beam group indicated by thedetermined first PMI.
 11. The apparatus of claim 10, wherein the atleast one processor is further configured to: determine a state of adownlink between the eNB and the UE based on an uplink reference signalreceived from the UE when the eNB operates in a time division duplex(TDD) mode, and determine the one first PMI among the plurality of firstPMIs based on the determined state of the downlink.
 12. The apparatus ofclaim 10, wherein the at least one processor is further configured to:receive, from the UE, a plurality of different CSI feedback respectivelycorresponding to a plurality of different CSI processes that arerespectively allocated the plurality of first PMIs, and determine theone first PMI among the plurality of first PMIs based on the pluralityof received different CSI feedback, and wherein the plurality ofdifferent CSI feedback each comprises information on a CQI as to the onefirst PMI allocated to a different CSI process corresponding to each ofthe plurality of different CSI feedback.
 13. The apparatus of claim 8,wherein the at least one processor is further configured to transmit aCSI reference signal (CSI-RS) to the UE, and wherein each of theplurality of CSI feedback is generated based on the CSI-RS.
 14. Theapparatus of claim 8, wherein the at least one processor is furtherconfigured to transmit, to the UE, the data modulated based on thedetermined MCS value by cyclically using the plurality of PMIs based ona designated device, and wherein the designated device is set to one ofa physical resource block (PRB) and a recoding resource block group(PRG).
 15. An apparatus of a user equipment (UE) in a wirelessenvironment, the apparatus comprising: at least one processor; and atleast one transceiver configured to be operatively coupled to the atleast one processor, wherein the at least one processor is configuredto: transmit, to an evolved node B (eNB), a plurality of channel stateinformation (CSI) feedback respectively corresponding to a plurality ofCSI processes that are respectively allocated a plurality of precodingmatrix indexes (PMIs), the plurality of CSI feedback each comprisinginformation on a channel quality indication (CQI) as to a PMI allocatedto a CSI process corresponding to each of the plurality of CSI feedback,and receive, from the eNB, data transmitted by cyclically using theplurality of PMIs, and wherein the data transmitted from the eNB ismodulated based on a modulation and coding scheme (MCS) value determinedbased on the plurality of CSI feedback including information on CQIs forall of the plurality of PMIs that are used for PMI cycling in eachsubband.
 16. The apparatus of claim 15, wherein the plurality of PMIs isrespectively allocated to the plurality of CSI processes based on aradio resource control (RRC) message comprising information on acodebook subset restriction.
 17. The apparatus of claim 15, wherein theplurality of PMIs comprises some of a plurality of second PMIsrespectively indicating beams comprised in a beam group indicated by onefirst PMI determined among a plurality of first PMIs respectivelyindicating a plurality of beam groups.
 18. The apparatus of claim 17,wherein the at least one processor is further configured to transmit, tothe eNB, a plurality of different CSI feedback respectivelycorresponding to a plurality of different CSI processes that arerespectively allocated the plurality of first PMIs, wherein theplurality of transmitted different CSI feedback each comprisesinformation on a CQI as to the first PMI allocated to a different CSIprocess corresponding to each of the plurality of different CSIfeedback, and wherein the determined first PMI is determined among theplurality of first PMIs based on the plurality of different CSIfeedback.
 19. The apparatus of claim 15, wherein the at least oneprocessor is further configured to: receive configuration information ona CSI reference signal (CSI-RS) from the eNB, and receive a CSI-RS fromthe eNB based on the received configuration information on the CSI-RS,and wherein each of the plurality of CSI feedback is generated based onthe CSI-RS.
 20. The apparatus of claim 15, wherein the data transmittedfrom the eNB is received by the UE by cyclically using the plurality ofPMIs based on a designated device, and wherein the designated device isset to one of a physical resource block (PRB) or a precoding resourceblock group (PRG).